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HUMAN PHYSIOLOGY 



change, whatever it is, does not develop simultaneously 

 throughout the neuron, but, starting from one point, be it 

 one end or the middle, travels or is conducted along. The 

 rate of conduction may be determined 



~Lst. By stimulating a nerve going to a muscle at two 

 points at known distances from one another, and measuring 

 the difference of time which elapses between the contraction 



Fio. 38. M, Muscle attached to crank lever marking on revolving drum. The 

 secondary circuit of an induction coil is connected with a commutator, with 

 the crossed wires removed so that the current may be sent either through 

 the wires going to the nerve at A far from the muscle, or at B, a point at a 

 measured distance nearer the muscle. On the drum, A represents the onset 

 of contraction on stimulating at A, and B the onset on stimulating at B. 

 To secure stimulation in each case with the drum in the same position, the 

 make and break of the primary circuit is caused by the point K touching 

 and quitting the point P. 



resulting from stimulation at each. (Practical Physiology, 

 Chap. VII.) (Fig. 38.) 



2nd. By taking advantage of the fact that the active 

 part of a neuron like the active part of a muscle is 

 electro-positive or zincy to the rest, and by finding how long 

 after stimulation at one point this electric change reaches 

 another point at a measured distance oft'. (Fig. 39.) 



The rate of conduction varies considerably, everything 

 stimulating protoplasmic activity accelerating, and every- 



